This invention relates to a catheter and trocar structure which enables simultaneous, bi-directional flow of fluids therethrough.
There exists a variety of catheter designs for use in injection or withdrawal of fluids from body cavities, ducts, vessels, or the like. Examples of some catheter or similar tubular designs are shown in U.S. Pat. Nos. 2,393,002, 3,459,189, 3,833,033 and 3,929,126. Typically, the catheters include a stylet or trocar inserted within the catheter to facilitate puncturing the body cavity, duct or vessel, and to provide support for the catheter. Once the catheter has been inserted into the body, the stylet or trocar is withdrawn to then allow either injection or withdrawal of fluid through the catheter.
In many treatment situations, it is desirable to introduce fluid into and withdraw fluid from the body simultaneously. One such situation is the withdrawal of blood from a blood vessel for treatment by an artificial kidney and then the reintroduction of the treated blood back into the blood vessel. In the typical manner of simultaneous withdrawal from and introduction of fluid into a body, two separate needles or catheters are utilized and this means two separate punctures must be made with the attendant discomfort, possibility for infection, damage to blood vessels, and trauma.
Single needle catheters have been suggested but the operation of such catheters, in most instances, is a type of ping-pong flow where fluid is alternately introduced into and withdrawn from the body. The disadvantage of this is that some of the fluid which may have just been introduced into the body may also almost immediately be withdrawn. This occurs because the entrance and exit for the needle in the body are at the same location. Also, higher flow speeds or quantities are required for the alternate introduction and withdrawal of fluid to achieve the same average rate of flow as could be achieved with a simultaneous introduction and withdrawal operation.
One catheter structure which has been proposed involves the use of concentric tubes in which an inner tube is used for introducing fluid into a body and the outer tube is used for withdrawing fluid from the body, or vice versa. One implementation of this arrangement is to first place a removable cutting tocar within the outer tube to facilitate insertion of the catheter into the body. Then, after insertion, the trocar is removed and the smaller inner tube is placed within the outer tube to enable introduction and withdrawal of fluid from the body. This implementation is cumbersome and time consuming, which necessarily increases the discomfort of the patient, and vulnerable to infection. Also, because of the concentricity of the two tubes, the passages through which the fluid flows, at least the passage between the larger tube and the smaller inner tube, present a significant flow resistance because of the low hydraulic radius. This increases the shear levels which, for blood withdrawal, causes greater damage to the blood.
It is generally desirable that while a catheter is being inserted into the body of a patient that fluid be prevented from flowing into the catheter. The single needle catheter, and concentric catheters generally make no provision for preventing such flow during insertion.